Electronic switching device



July 28, 1953 R. B. TROUSDALE ELECTRONIC SWITCHING DEVICE Fild Jan. 27, 1950 s Sheets-Sheet 1 Ju y 8, 1953 R. B. TROUSDALE 7,

ELECTRONIC SWITCHING DEVICE Filed Jan. 2'7, 1950 3 Sheets-Sheet 5 asz me E arwde Source,

IN V EN TOR.

Babe/'23. fi'ousa'ale Y Patented July 28, 1953 ELECTRONIC SWITCHING DEVICE Robert B. Trousdale, Rochester, N..Y., ass'ignorto Stromberg-Carlson Com New York pany, a corporation of Application January 27, 1950-, Serial No.--140,929

This invention relates to an electronic-switching device and more particularly to an electronic switching device for controlling an electric circuit including an improved time delay feature for preventing inadvertent or unintentional switching from taking place. Specifically the instant application is a continuation in part of 'copending Trousclale application Serial No. 70,252, filed January 11, 1949, now abandoned.

In many situations it is desirable to provide an electronic switching arrangement in which pow,-

er is automatically applied or removed in a controlled manner. This is particularly true where numerous electron discharge valves are employed as in radio receivers, sound amplifiers, and com- .5.

munication circuits utilizing electron discharge devices, since it is desirable to avoid unnecessary current drain during idle periods of the equipment by switching oi? the anode potentials.

A specific application of the present invention is in the telephone system art where it is, desirable to provide a control arrangementfir switching control potentials in response to the removal the receiver from its hook bythe calling party. In an electronicsystem where relays are replaced by electron discharge devices, it is furthermore desirable that these control potentials be removed when the receiver is replaced on the hook to avoid unnecessary current drain. I (in the other hand, it is essential that these control potentials remain in effect for a predetermined period after the receiver is replaced on the hook in order that hook switch flashing and the like do notcanse the circuit which is being prepar ed between thecalled and calling party .tobefintercircuit for applying and removing potentials in response to a predetermined "control;

It is another object of the present invention to provide an electronic switching arrangement'including an improved time delay 'feature ior'preventing prematureremoval of the control potentials. I n -Still another object of the present inventionis -to-provide an electronic switching devicein which 27 Claims. (c1. 250-427) 1 2 the-application'or removal of signal pulses renders the switching device effective or ineffective'to control suitable potentials and wherein a predetermined time delay in the switching operation is provided to prevent removal of the control potentials due to momentary lapses in the supply of pulse signals.

1 Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the'invention will be pointed out with particularity in'the claims annexed to and forming a part of this specification.

For a better understanding of the present invention, reference may be had to the accompany- -ing drawings in which:

Fig. 1 is a schematic diagram illustrating one embodiment of the present invention;

Fig. c'illustrates a modification of Fig. 5.

V lhe switching device of the present invention contemplates the employment of a plurality of electronic discharge devices connected in a control circuit and operative in response to the supply of a pulse signal current to remove from or apply-to an-associated 'circuit suitable control potentials. By Way of example, the switching circuit may be caused to-operate and apply the control potentials to anassociated circuit such forexample 'asa load circuit, in response to the receipt of periodic positive current pulses. Upon the cessation of the receipt of such. current pulses, means are provided to cause the switching. device to: remove thepotentials"applied to the associated apparatus but not until the elapseof a predetermined time delay, thereby to prevent premature removal of the potentials applied to the associated circuit.

While the electronic switching circuit of the present invention is particularly well adapted for use-in connection with an electronic telephone system for rendering effective and ineffective connectors for connecting the called and calling circuits to provide a signal link and to prevent premature release of such-link due to various factors, it will-be understood that the electronic switching device of the present'invention has "numerous other applications 1 and nlay e employed "wheiiver the application" or re"- moval of switching potentials in response to the receipt or absence of pulse signals is desired.

Considering now the embodiment of Fig. l of the drawings which at present is considered to be the pref-erred embodiment, there is illustrated an electronic switching circuit generally designated at Ill for controlling the potentials applied to an associated utilization circuit generally designated at H, from a-I-B source of potential I2, which generally is a source of anode potential, through an electronic switch It serially connected between the source I2 and the output il As illustrated the source I2 provides the anode supply for the utilization circuit I I when the electronic switch is operative to conduct current therebet'ween. The electronic switch preferably comprises an electron discharge valve containing anionizable medium generally referred to as a gas tube or thymtron designated as I3 whereby when rendered conductive it has a relatively low and constant voltage drop. In the preferred embodiment, shownby the drawings, the control of the potentials supplied to the utilization circuit II is accomplished in response to the absence 'or presence -of pulse signals supplied to the electronic switching circuit Iii from a suitable pulse input circuit generally designated at I4. The pulse input circuit is capable of supplying pulse signals of the type shown in Fig. 2 of the drawings, which pulse signals may be discontinued or initiated in response to suitable control means for the pulse input circuit which forms no part of the present invention. For a particular application in which the present switching circuit has been found to be especially efiective, the switched potentials supplied to the output or utilization circuit I I in response to the pulse signals of Fig. 2 may take the form shown in Fig. 3 of the drawings although from the detailed description included hereinafter it will be understood that the output of switched potentials may be controlled in various manners.

In accordance with the present invention, the electronic switching circuit It in addition to the electron discharge valve I3 further comprises electron discharge valves I5 and I6. The electron discharge valve It comprises a timing tube, and the electron discharge valve l6, as will become apparent from the following description, functions as an extinguishing tube for interrupting the space discharge current through the electron discharge valve I3. Preferably and for a specific application for which the electronic switching circuit Ill has been found to be especially efiective, the electron discharge valves I3, I5 and I5 are highly sensitive thyratrons such as, for example, the RCA commercial type 5696, each comprising an anode IT, a cathode I8, a control electrode I9 and a screen grid 26. For reason which will become apparent as the following description proceeds, the electron discharge valve I5 is provided with a filament 22 connected to a separate heater supply source generally designated at 23 through a suitable filament transformer 24.

In order to cause operation of the switch tube I3 in response to pulse signals supplied thereto from the pulse input circuit I4, the control electrode I9 of the electron discharge valve or switch tube I3 is connected to the pulse input circuit I4 through a suitable coupling capacitor 25. A suitable negative bias potential is also supplied to the control electrode I9 of valve I3 from a terminal 26 connected to a source of negative potential through a voltage dropping resistor 21 and a current limiting resistor 28. The terminal of the voltage dropping resistor 21 remote from the terminal 26 is connected to ground generally designated at 29 through a suitable resistor 38. The plate or anode of the electron discharge valve I3 is, of course, directly connected to the anode potential source I2. The plate circuit of the switching tube I3 further includes a cathode resistor 32 connected between the cathode IS and the ground terminal 33. When the electron discharge valve I3 fires to produce space current flow therethrough, the potential of the source I2, except for the voltage drop across the tube I3, which is relatively low, appears across the cathode load resistor 32. For the indicated source of potential I2, the voltage across the cathode load resistor will be approximately 148 volts. Preferably a suitable neon indicator 34 serially arranged with a resistor 35 is connected across the cathode load resistor 32 for the purpose of providing a visual indication of the condition of the switch tube I3. When the visual indicator is energized it provides an indication that the switch tube I3 is passing space current and applying control potential to the associated load circuit I I.

The screen grid 20 of the electron discharge valve or switch tube It is connected to the oathode I8 in the conventional manner. The potential of the cathode load resistor 32 is connected to the associated output circuit I I through a suitable filter comprising the high frequency choke coil 38 and a by-pass condenser 39 connected to ground as indicated at 19.

From the above discussion it will be apparent that by virtue of the fact that electron discharge device I3 is of the gas type, such as a thyratron, the control electrode Ill loses control once that space discharge current flows, and thereafter the presence or absence of positive pulses supplied to the control electrode I9 through the coupling capacitor 25 cannot directly afifect the ionized condition of the tube #3. It will be apparent that the positive pulses applied to the control electrode I8 through the coupling capacitor 25 overcome the negative bias voltage from the terminal 26 in order to cause firing of the tube l3.

In accordance with the present invention, the cathode load res stor 32 following firing of the tube I3 provides the source of plate potential for the electron discharge valves I 5 and I6. To this end the cathode load resistor 32 has its cathode terminal connected to the plate I'I of the tube I6 through a suitable current limiting resistor 43 and to the plate I? of the electron discharge valve I5 through a timing resistor 54. The plate ll of the electron discharge valve i5 is also connected to a terminal 41 of a timing condenser 45 whose other terminal is connected to ground as indicated at 48. The cathode I8 of the electron discharge valve IE is connected to ground designated as 48 through a cathode load resistor 49. The cathode I8 of the electron discharge valve I6 is also connected to the cathode terminal of the cathode load resistor 32 through a suitable condenser 50. The control electrode I9 of the electron discharge valve IB is connected directly to the terminal 4'. of the timing condenser 45. The screen grid 20 of the electron discharge valve I6, on the other hand, is connected directly to the cathode Ill. A suitable by-pass condenser 52 connects the plate H to ground as indicated at 53.

The timing tube I5, on the other hand, has its cathode connected to a terminal 54 interposed between voltage dividing resistors 55 and 56 which are serially connected between the negative terminal of a source of potential 57 and ground generally designated at 58. A' suitable by-pass condenser 60 connects the screen grid 20 and terminal 54 to ground58.

In order to fire the tube I5 in response to the receipt of input pulses from the input circuit I4, the control electrode I9 of valve I5 is also connected to the input signal source I4 through-a suitable coupling capacitor 6|. A suitable negative biasing potential illustrated as obtained from the source 57 is also applied to the controlelectrode I 9 of valve l5 through a suitable current limiting resistor 62. Considering now briefly the operation of the switching circuit Ill, it has been pointed out above that the switching tube I3 is fired under the influence of the pulses supplied from the pulse input circuit M. When space current now through this' tube is established an operating anode potential of approximately 140 volts' appears at the cathode end of the resistor 32. After this tubeis fired deionization thereof is under the control of the two associated tubes I5 and I6. More specifically, the extinguishing tube I6 is provided'to deionize the tube I3 when the pulse signals from the source It are terminated while the tube I5 is provided to prevent undesired deionization of the tube I3 during brief discontinuities in the pulse signal input which in a telephone system,'for example, would occur during hook switch flashing intervals and the like.

The manner in which the above mentioned functions are carried out in the circuit In may best be explained by reference to Figs. 2, 3 and 4 of the drawings, the significance of which is pointed out more fully below. Normally, i. e., with the circuit I inactive, the condenser 45is completely discharged through the resistors 44 and 32 so that the terminal 41 thereof is'at sub stantially'zero potential. Also, with the circuit It inactive, the negative 100 volts impressedbetween the bias-terminal and'ground by the bias-"potential source is divided between the two resistors55 and 55in the ratio of five volt's across the resistor 55and 95 volts'across' the'resistor 56. Thus, the cathode of the tube I5 is normally maintained at a potential which is '95 volts-negative with respect toground. Due'to the presence of this high negative potential 'upon the cathode of thetube I5,"it=is necessary to provide" a separate heater supply source for the --filamentary heater- 0f the tube as-descr-ib'e'd above in order to prevent arcing between the tube heater 22 and cathode I8 which wouldresult in destruction of the tube heater 22. This is accomplished by providing' the separate current supply transformer 24 having its primary winding connected to an appropriate source 23 of alternating currentand its secondar winding bridged by the heater 22 of the tube I5. -This winding is connected tothe negative terminal of the 100 volt bias potential source so that the heater is effectively maintained at a potential approximately five voltsnegati've with respect to the tube cathode. This arrangement positively precludes any arcing between the cathode and cathode heater of the tube I5. When the switching tube l3 fires inthe manner explained above, the condenser52 is charged to the full value of the voltage across the-resistor 32*thrOugh the resistor 43 and operating anode potential is supplied to the tube I6. Also,"the condenser 58 is charged 'through the cathode resistor '49 to the full "value of' thevoltage across the resistor 32. Charging of the condenser" 5ll over this path drives the cathode terminal of the register ng highly positiveldurin'g the initial pore 6 tion of the charging interval. Concurrently with charging of the condenser 50 a charging path for the condenser 45 is established from the cathode terminal of the resistor 32 through the timing resistor 44. Initially, the major portion of the charging voltage appears across th resistor 44 and a very small portion thereof appears across the condenser '45. Similarly, the major portion of.the charging voltage for the condenser 56 initially appears across the cathode resistor 49 immediately after the tube I3 fires. Thus, during the initial portion of the condenser charging interval, the control grid I9 of the tube I6 is held at ground potential whereas the cathode I8 of the tube I6 is driven highly positive. The grid I9 of the tube I6 is thus efiectively biased negativerelative to the tube cathode l8 by an amount equal to the voltage drop across'the resistor 49. This bias prevents the tube I E from firing.

As explained above, normally the grid of the tube l5'is biased approximately five volts negative relative to the tube cathode by the voltage across the resistor 55. Thisbias voltage prevents the tube I 5 from firing in the absence of positive pulses supplied through the coupling capacitor 6I' from the pulse input circuit I4. However, iinmediatelypositive pulses are gated through this'capacitor filfthey are impressed upon the control grid IQ of the'tube l5 and serve to drive this control grid positive relative to the tube cathode and fire the" tube. 'It will thus be apparent that the tubes I5 and I3 are fired substantially simultaneously. When the tube I5 is fired, current flows through this "tube andthe condenser '45 in a circuit which extends from the grounded terminal of the resistor 56 through the condenser 45, the space current path through the tube I5 and the resistor 56. 'Thus, the voltage across the resistor 55 less the voltage drop through the tub'e'l5 i's impressed across the condenser 45 immediately the tube I5 fires. As a consequen'ce'the capacitor terminal is driven approximately 'volts'negative with respect to ground. 'In Fig. 4 of the drawings, this negative voltage rise of the terminal 41 is indicated along the portion C1 of the potential curve A of the terminal 41. i The negative potential thus developed atthe terminal 4''! -is directly'impressed uponthe 'controlgrid of thetub'e' I6 to'bias this grid highly negative with: respect to the cathode of the tube and thus pr'event the tube from'firing regardless of the voltage across the cathode'resistor '49 Wh'en'the' voltage across the condenser lS rea chesa value of minus 80 volts','-current flow through the tube I 5 drops to the extinction point ahd'i's' interrupted. The c'o'ndenser'45 now starts to charge through the resistor 44- tending' to approach the positive potential of volts across the re'sistor'32 indicated bythelineEin Fig.4 of the drawings. The charging rate of the condenser-" 45 is obviously determined by' the' time constant of the series" circuit"comprising this condenserandtheresistor 44. In this regard," it is pointed out that the condensert5 preferably has a very large capacitance' value, of the order of "0:1 microfaradfand the resistor'M" preferably hasa very large resistance" value" of theorder of 7 megohms, su-ch' thatth'e time constant of the circuit is'very' long and the charging rate of the condenser 45 1s correspondingly "10w. Specifi cally, the i condenser 45 sta'r'ts "to charge at" the rate indicated bythe curve A1 in Fig, 4. it charges, the? negative potential of the terminal at isac rresp dine y educedas indicated by'the segment Bifofthe ,c'urveiA 'of"'F'ig. "4.' When the negative potential of this terminal 4? is reduced to a value of approximately 60 volts negative, the voltage across the tube 15 is increased to a value at which this tube refires. When the tube i5 refiles, the voltage across the condenser 45 instantly rises in a negative direction to a value of 80 volts negative as indicated by the curve segment C2 in Fig. 4 to again produce deionization of the tube E5. The described relaxation type of operation of the tube 15 and condenser 41 continues in the manner indicated by the curve segments B2, C3, B3, C4 so long as signal pulses continue to be received through coupling capacitor 6| from signal source 14.

In automatic telephone apparatus of the type disclosed in the above mentioned copending Morris and Trousdale application, the production of input signal pulses is arrested during the return stroke of the telephone dial and also when the hook is actuated as during hook flashing intervals. Also in other systems it is common to have lapses in the pulse signal source. Such a lapse in the pulse signal from source It is indicated between times t2 and is of Fig. 2 of the drawings. During this interval the tube 15 cannot refire after it is first extinguished during the initial portion of the pulse lapse period. Accordingly, and again referring to Fig. l, the condenser 45 charges through the resistor 46 for the duration of the impulse in the manner indicated by the curve segment B4. Due to the long time constant of the condenser charging circuit, the indicated pulse lapse period is not long enough to charge the condenser to the value D at which the negative bias on the control grid l9 of the tube It becomes insufficient to prevent this tube from firing. When the pulse lapse period from 162 to is ends and input pulses again occur as at time is in Fig, 2, the tube l5 immediately fires to recharge the condenser 45 and raise the potential of the terminal 4'5 in a negative direction to the negative 80 volt value as indicated by the curve segment C5. During the succeeding period following time t: in Fig. 2 of the drawings when the pulses again occur, the described relaxation operation of the tube 15 and condenser 45 is resumed in the manner explained above as indicated by the curve segments B5, C6, B and C1 of the curve A of Fig, 4. In the event that the present invention is applied to a telephone system of the type referred to above, the input pulse signals would continue so long as the receiver at the calling station is oil hook, and during this time the described relaxation operation will also continue. In Fig. 4 the curve segments B7 and Cs of the curve A illustrate the last relaxation cycle which occurs before the pulses are terminated at time to. as, for example, in an automatic telephone system when the call is abandoned or terminated.

When the input circuit ceases to produce pulses applied to the control electrodes 59 of electron discharge valves l3 and I5, the condenser d is permitted to charge through the resistor 44 from the cathode resistor 32 so "that the negative potential of the terminal 4! is decreased along the curve segment B3 of Fig. 4. When this potential reaches the critical value D with a corresponding reduction of the bias on the control grid of the tube 46, this tube fires. In firing, the tube it instantly discharges the condenser 52 through the space current path thereof and the resistor '49. Thus, 'a voltage of approximately 130 volts is developed across the resistor 49. This voltage spike is additivelycombined with the 140 volts across the charged condenser 58 to produce a voltage across the cathode resistor 32 of approximately 270 volts. Thus, at time ts the cathode of the tube [3 is driven positive relative to the anode of this tube and space current flow through the tube is interrupted. Referring to Figs. 3 and 4, the transient spike occurring at time is and developed across the resistor 32 is indicated at I at the end of the switched +B potential curve G in Fig. 3 and the change in potential at the terminal point ll produced by the same transient voltage is indicated at E along the potential curve A of Fig, t. When space current flow in the tube 13 is thus interrupted, the condenser 55 discharges through the two resistors 32 and 49, following which the voltage across the resistor 32 drops to zero. Thus, operating anode potentials are removed from the utilization circuit H.

From the preceding explanation, it will be understood that the switching circuit of Fig. 1 functions positively to prevent false cut off of the potential to circuit ll during momentary pulse lapses of the signal source i i.

Referring now to the modification of Fig. 5 of the drawings, there is shown an electronic switching circuit intended to be utilized to furnish the anode supply for a suitable utilization circuit and this electronic switching circuit employs both high vacuum and gas type electron discharge valves. The anode suppl is indicated by the numeral "H and the utilization circuit is illustrated by the numeral 72. In order to switch the anode supply with respect to the electron discharge devices in the utilization circuit 72, there is provided an electrical switch 13 in series with the anode supply "H and the utilization circuit 12. The electrical switch preferably comprises an electron discharge device '53 of the gas containing type which will continue to conduct, once it is triggered on, until the oathode-to-anode potential is made insufficient to continue the current flow through the tube. A device of this type is desirable because such devices as was mentioned above had a relatively low and constant internal voltage drop.

Anode I l of device i3 is illustrated as being connected directly to the anode supply ii, and the cathode i5 is illustrated as being connected to the utilization circuit '52 through a suitable filter comprising resistor i6 and capacitor 16a. The control electrode TI of device 73 is suitably biased beyond cutoff as by means of a suitable source of negative potential. There is illustrated a resistor it connected between a suitable source of ne ative potential and ground, and the control electrode 1? is connected to a suitable point on that resistor.

For the purpose of triggering the discharge device 13 there is provided a signal source 13 which preferably is a source of a train of pulses or the like. Between the source 78 and the switch '13, there is interposed a control element which maybe an electron discharge device 8!] illustrated as being of the triode type. The anode 8! of discharge device 30 is connected to a suitable source of +13 potential through a suitable inductance 82. Cathode 83 of device 88 is connected to ground, and signals from source 19 are applied to control electrode M of device through a suitable coupling capacitor 85. The discharge device as is normally biased beyond cutoff by connecting the control electrode 84 to a suitable source of negative biasing potential, as for example, to a point on potentiometer or resistor 86 connected between ground-and a suitable negative potential. I

The source of signal potential or control quantity 19 is arranged to deliver positive-going pulses to discharge device 80 of sufficient amplitude to render conductive device 89. The presence of inductance 82 in the anode circuit causes a transient to be set up in the output circuit of device 80 which, in eiTect, prolongs the duration of the signal pulses and strengthens the effect of the signal pulses. The transients are applied to the control electrode 11 of--device 13 "througha suitable coupling capacitor 81. Theappearance of a sufficiently positive potential on-control elec= trode 11 causes the device 13 to become con ductive to connect the anode supply H 'to the utilization circuit 12. With the type of device employed, the control electrode 11 loses control and device 13 continues to conduct until its anode-to-cathode potential is brought below the current-sustaining'level. f 1

Means are provided *for disconnecting the anode supply at the' en'cl -"Of the p'eriod when source 19 produces a pulsesignal- For this purpose, there is provided a series combination'of resistor 89 and capacitor 88, resistor 89 being illustrated as connected to cathode 15 of discharge device 13 while capacitor 88 is illustrated beingconnected btvveen'rsistor 39 and ground. With the arrangement described, ithe switcl'iy'eld' potential tends to capacito 88 through resistdr89. e 4m 7 Meansare provided for-"limitingf'fthe charge; attained by capacitor; 8 3' during the;;time when; it'is desir'dto connect theanodepot ntial'szource 1 I 'to "the utilization QllCl1it12.f Ei'g. there i's illustrated for this purpose an" lectron dis-iv charge device 9| "shown as being of" thejjtriode typehaving an anode 92 connected to the "ungrounded side of capacitor 88 and',"therefore, to the anode potential lead or conductor 90 through series resistor 89. The cathode 93'is grounded and the control electrode .94, of. ,device .9I is con-. nected to a suitable source of biaspotential; In F ig. 5 control electrode or grid 9Ilis connected to'a pointon a suitable resistor 95 which in turn is connected between ground and a suitable source of negative potential. i With the arrangement shown, and in the absence of signal'pulses-"iromthe source 19, dis charge device 9| is nonconducti v e. The-transients appearing in the output of device 80 are applied to control electrode 94 througha suitable coupling capacitor 96' and by choosing-properlylthe-valuepf outoiT bias, device9l is renderedv conductive upon the appearance of signal-energy;

thereby shunting capacitor-88..= With-a pulse input, device 9| becomes non-conductivebetween.-

pulses and capacitor 88 begins to charge, but the next pulse againwdischarges the capacitor. However, upon the cessation of signal energy for a predetermined time, discharge device9I- remains non-conductive and the shunt across capacitor 88 is removed for agtirne suflicient to allow the capacitorl88 toeharge uninterruptedly, thr'oughresistor 89 toward the potential of -con.-,

ductor 90. The rate of charge depends upon the time-constant of" the resistance-capacity. circuit;

comprising resistor 89 and capacitor 88. In order to adjust the time- 0f charging, be made variable as illustrated" Means are providedfor utilizing the charge 9.. 'sfi eqii tr 88 J3 n i$b.. :the. dischar e; ml i ev e." ameih r ore. to onenlthe.

resistor 89 may ranged to provide relaxation electrical-switch. This ,means includesa dis-1 charge device 91, preferablyof. the gas-filled type; and which may be a cold cathode device. The control electrode 98 of device 91 is connected to the ungroundedside of capacitor 88 .The anode 99 of device 91 is connected to a suitable'source of positive potential through a resistor I90 shunted by a capacitor IOI.- Cathode I92 of device 91 is connected to ground through a suit able resistor I03; Any potential established across resistor I03 is applied to the cathode 15 of'discharge device 13 through a suitable cou pling capacitor III I. Y When "the potential across capacitor 88 reaches a sufilciently highvalue; discharge device-91 is rendered conductive and, momentarily,'substan tially' the entire jresistive drop in the anodeto-cathQde circuit exclusi'veof tube drop appears across resistor I03. Capacitor I04 was'previously charg'edto the potential of anode supply lead 90. The sum of thep-otentials'acrossresistor I93 and capacitor I04 is applied'to cathode 15 of discharge device 13"and'the sum being in excess of the internal drop o'f" discharge device 13, the potentialat cathode 15 is raised suficiently to render discharge device 13 non-conductive.

The presence of capacitor IUI results in a gradual shift of potential fro-macross resistor I03 to-capacitor IIlI and eventually the difference in potentialbetween anode 99-and cathode "I92 becomes *too small-"'t'ocontinue conduction and discharge device 91bt'orhes phon c-conducting. At this p-ointjthe system isresetior the neat con ductive period; v in Fig. 6 there is illustrated a modification'of the present invention in'which Electron diSChalIgG device 9| is replaced by'an electron discharge device lll8 of the" gaseous -dischargetyp'e. Gas discharge device I06 is.'substituted for the cold cathode tube 91 and'servesa's a switching tube which, when ignited, momentarilysupplies anode currentffroini CapaeitO-MUIJJ nisiljarge device biased beyond'eutofi while the circuitin ewc nso -an m S'arlid sm I01 of gaseous aistnarge'sevic lfl fiibyjmeans of the negative potential atcath delIilil; or discharge" device :I Discharge fdevice lqfi is repeatedly triggered by the input pulses ampli fie d .by discharge device and the ringing coil 82 and applied to'the control electrode II9 of discharge device I98 through coupling capacitor 96. Y

As indicated, discharge-device I 98 is agaseous discharge tube and the circuit constants are aroscillator operation. The tube 498, however, is arranged so that 'it'isnot completely self-oscillating but requires trig-- geringby the incoming signal pulses.- There fore, as-long--assignal pulses persist,'dischar'ge device I08 oscillatesand*capacitor' I H connected between anode I 01 and groundischarged in a negative'direction to-maintain discharge device I96 cutoff.-

'Whensignal pulses cease, di'schar'ge device I98 no longer tial at central electrode IIZ'of discharge device I05 gradually becomeslmore and inore positive until finally discharge device I96 is rendered conductive to extinguish conduction through discharge device 13 which removes the potential supplied to utilization circuit 12 and disables the associated discharge device circuits.

By employing a gaseous discharge device I08, the circuit functions completely once the circuit iis triggeredhy an-- ihcom-ingsignalpulse dead-coo ven though the triggering pulses may be extremely short. Therefore, the modification shown in Fig. 6 is less affected by variations in signal pulses, A gaseous type discharge device [65 has been used instead of the cold cathode tube 91 illustrated in Fig. 5, because of its more reliable operation and higher peak current.

While there have been illustrated and described several embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United "States is:

1. In a communication system, a source of potential, utilization means, an electron discharge device having an anode a cathode and a control electrode, the anode-cathode path of said discharge device interconnecting said potential source with said utilization means, a signal source connected to said control electrode, said device being rendered conductive in response to the production of a signal at said signal source thereby to connect said source of potential to said utilization means, and means jointly responsive to the flow of current through said dis- 9 charge device and the continued absence of a signal at said signal source for a predetermined time interval for establishing an electrical quantity for rendering said discharge device non-conductive.

2. In a communication system, a source of potential, utilization means, an electron discharge device having an anode a cathode and a control electrode, the anode-cathode path of said discharge device interconnecting said potential source with said utilization means, a signal source connected to said control electrode, said device being rendered conductive in response to the production of a signal at said signal source thereby to connect said source of potential to said utilization means, a capacitor, means responsive to the flow of current through said device for charging said capacitor in a predetermined manner and operative in the event of continued absence of signals at said signal source for a predetermined time interval to charge said capacitor to a predetermined charge, and means responsive to said predetermined charge on said capacitor for rendering said discharge device non-conductive.

3. In a communication system, a source of potential, utilization means, an electron discharge device having an anode a cathode and a control electrode, the anode-cathode path of said discharge device interconnecting said source with said utilization means, a signal source connected to said control electrode, said tential, utilization means, an electrical switch comprising an electron discharge device interconnecting said source and said utilization means, a control electrode for said device, a control signal source connected to said control electrode, means responsive to the appearance of signal energy from said signal source on said control electrode for causing conduction through said electron discharge device and the application of potential to said utilization means, a capacitor, means responsive to the flow of current through said electron discharge device for charging said capacitor in a predetermined manner, means responsive to the production of signal energy by said signal source for limiting the extent to which said capacitor is charged in said predetermined manner, the absence of signal energy from said signal source permitting said capacitor to charge uninterruptedly in said predetermined manner, and means responsive to the charge developed across said capacitor when charged uninterruptedly in said predetermined manner for a predetermined time for extinguishing the flow of current through said discharge device.

5. In a communication system, a source of potential, utilization means, an electrical switch comprising an electron discharge device interconnecting said source and said utilization means, a control electrode for said device, a control signal source connected to said control electrode, means responsive to the appearance of signal energy from said signal source on said control electrode for causing conduction through said electron discharge device and the application of potential to said utilization means, a capacitor, means responsive to the flow of current through said electron discharge device for charging said capacitor in a predetermined manner, means comprising a second electron discharge device responsive to the production of signal energy by said signal source for limiting the extent to which said capacitor is charged in said predetermined manner, the absence of signal energy from said signal source permitting said capacitor to charge uninterruptedly in said predetermined manner, and means responsive to the charge developed across said capacitor when charged, uninterruptedly in said, predetermined manner for a predetermined time for extinguishing the flow of current through said discharge device.

6. In a communication system, a source of potential, utilization means, an electrical switch comprising an electron discharge device interconnecting said source and said utilization means, a control electrode for said device, a com trol signal source connected to said control elece trode, means responsive to the appearance of signal energy from said signal source on said control electrode for causing conduction through said electron discharge device and the application of potential to said utilization means, a capacitor, means responsive to the flow of current through said electron discharge device for charging said capacitor in a predetermined manner, means, comprising a second electron discharge device responsive to the production of signal energy by said signal source for limiting the extent to which said capacitor is charged in said predetermined manner, the absence of signal energy from said signal source permitting said capacitor to charge uninterruptedly in said predetermined manner, and means comprising a third electron discharge device responsive to the charge de- 13 veloped across said capacitor when charged uninterruptedly in said predetermined manner for a predetermined time for extinguishing the flow of 1 current through said discharge device.

'7. In combination, a potential'supply circuit, a utilization circuit, an electronic switch comprising a first electron discharge valve for connecting said supply circuit to said utilization circuit, said valve having a control electrode, a signal source connected to said control electrode, the receipt of a predetermined signal fromsaid signal source rendering said electronic switch efiective to interconnect said supply and utilization circuits, a second electron discharge valve having a control electrode, means for connecting the control electrode of said second valve to said signal source thereby to render said second valve conductive substantially simultaneously with said first valve, circuit means responsive to the flow of current through said second valve 'for rendering said second valve non-conductive, means responsive to the flow of current through'said firstvalve while said second valve is non-conductive for rendering said last mentioned means ineffective whereupon said second valve is again rendered conductive following receipt of a predetermined signal from said signal source, a third electron discharge valve, and means forrendering said third electron discharge valve conductive only after said second discharge valve remains nonconductive for a predetermined time following conduction thereof, and means for connecting said third valve in circuit with saidfirst valve to render said first valve non-conductive upon firing of said third valve.

8. In combination, a potential supply circuit, autilization' circuit, an electronic. switchscomprising a first electron discharge valve containing an ionizable medium for connecting said supplycircuit to said utilization circuit, said valvehaving a control electrode, a-signal source-connected to said control electrode, the receipt of a predetermined signal from said signal source rendering said electronic switch effective-to intercon nect said supply and utilization circuits, a second electron discharge valve containing an ioniza'bl'ei medium having" a control *electrode, 1 means for. connecting the control electrode-'of- 'said second valve to said signal source thereby te -render saidsecond valve conductive substantially-simultaneously with said first valve, circuit means responsive to the flow of current through saic'I second valve for rendering said second valve'non conductive, means responsive to the flow of current through said first valve while-said second'valve-is non-conductive for rendering said last' mentioned means ineffective whereupon saidsecond' valveisagain rendered-conductive following receipt of a predetermined signal from said-signalsourca'a third electron discharge valve contain-ing an ionizable medium, and means'fo'r rendering said third electron discharge --va'lvecon'ductive-' only after said'second dischargevalve remains-"non conductive for a predetermined time following conduction thereof, and .meansi for connecting utilization circuit, an electronicswitch compri ing a first electron discharge valve, for connecting said supply circuit to said utilizationcircuit, said valve having a coritrol'elc't'rode, a signal source connected to said control electrode,'tlie receipt of rendering said electronic switch effective to inter-2 connect said supply and utilization circuits, a second electron discharge valve having a control electrode, means for connecting the control elec trode of said second valve to said signal source,

thereby to render said second valve conductive substantially simultaneously with said first valve, circuit means responsive to the flow of current through said second valve for rendering said second valve non-conductive, means responsive to the flow of current through said first valve While said second valve is non-conductive for rendering; said last mentioned means ineffective whereupon saidJsecond valve is again rendered conductive following receipt of a predetermined signalfrom said signal source, and means forrendering said first valve non-conductive.

'liliIncornbination, a'potential supply circuit, a utilization circuit, an electronic switch comprising'a first electron discharge valve for connecting said supply circuit to said utilization circuit', said valve having a-control electrode, a-

signal source connected to said control electrode, the receipt of .a predetermined signalfromsaid signal source rendering said electronic switch effective'to interconnect said supply and utilization circuits, a second electron discharge valve having a control electrode, means -for connecting the plate circuit of said second valve in series with said first valve means for connecting the control electrode of said secondvalve to said signal source thereby to render said second valve conductive substantially simultaneously with said first valve, circuit means responsive-to the fiow of current through said second valve-iorrendering said second valve non-conductive; means 7 responsive to the flow of current through said first valve while said second valve is non-conductive for rendering said last mentioned means ineffective whereupon said second valve is again rendered conductive followingreceipt of a predeterminedsignal-from said signal source, a third electron discharge valve, and means for rendering said third electron discharge valve conductive only after said second discharge valve remains non-conductive for a predetermined time following conduction thereof and-means for connecting aidthird valve in'circuit with said-first valve tolrender said first valve non-conductive uponfiring'of said third valve. 1

ll. In combination,-a potential supply circuit,

antiliz ation circuit, an electronic switch comprising a firstelect'ron discharge valve for connecting said supply circuitto said utilization circuit-said valve having a control electrode, a signal source connected to said control electrode, the receipt of al predetermined signal from saidsignal sourcerenderingsaid electronic. switch effective to in. terconnect said supply and utilization circuits, a secondelectron discharge valve having-a controlelectrode, means for :connecting the control I elec.

trode of said secondvalve tosaid signal source thereby to render said second valve-conductive substantially simultaneously with said first valve, circuit means responsive to the flow of. currentthrough said second-valve-ior rendering said second-valve noneconductive, means responsive to the flow of current through said first valve while said second valve is non-conductive for rendering said last mentioned means ineffective wheresignal '-f r-om" said signal source,- a third electron Y I discharge valve havfirigjts platecircuit'colinected" a predetermined'signal from "said signarsource ingseriesrwith"saidiflrst valve;"andmeans for'i rendering said third electron discharge valve con-. ductive only after said second discharge valve remains non-conductive for a predetermined time following conduction thereof, and means for connecting said third valve in circuit with said first valve to render said first valve non-conductive upon firing of said third valve.

12. In combination, a potential supply circuit, a utilization circuit, an electronic switch compris ing a first electron discharge valve for connecting said supply circuit to said utilization circuit, said valve having a control electrode, a signal source connected to, said control electrode, the receipt of a predetermined signal from said signal source rendering said electronic switch effective to interconnect said supply and utilization circuits, a second electron discharge valve having a control electrode, means for connecting the plate of said second valve to the cathode of said first valve, means for connecting the control electrode of said second valve to said signal source thereby to render said second valve conductive substantially simultaneously with said first valve, means comprising a capacitor connected to the plate of said second valve and adapted to be charged in a predetermined manner in response to current flow through said second valve to render said second valve non-conductive, means for charging said capacitor in a different predee termined manner while said second valve is non conductive to permit said second valve to be rendered conductive in response to the receipt of a signal from said signal source, a. third electron discharge valve, and means for rendering said third electron discharge valve conductive only after said second discharge valve remains. nonconductive for a predetermined time following conduction thereof, and means for connecting said third valve in circuit with said first valve to render said first valve non-conductive upon firing of said third valve,

13. In combination, a potential supply circuit, a utilization circuit, an electronic switch comprising a first electron discharge valve for connecting said supply circuit to said utilization circuit, said valve having a control electrode, a signal source connected to said control electrode, the receipt of a predetermined signal from said signal source rendering said electronic switch efiective to interconnect said supply and utilization circuits, a second electron discharge valve having a control electrode, means for connecting the plate of said second valve to the cathode of said first valve, means for connecting the control electrode of said second valve to said signal source thereby to render said second valve conductive substantially simultaneously with said first valve, means comprising a capacitor connected to the plate of said second valve and adapted to be charged in a predetermined manner in response to current flow through said second valve torender said second valve non-conductive, means for charging said capacitor in a difierent predetermined manner while said second valve is non-conductive to permit said second valve to be rendered conductive in response to the receipt of a signal from said signal source, and a third electron discharge valve for extinguishing the current flow through said first valve.

14. In combination, a potential supply circuit, a utilization circuit, an electronic switch comprising a first electron discharge valve for connecting said supply circuit to said utilization circuit, said valve having a control electrode, a signal source connected to said control electrode,

16 the receipt of a predetermined signal from said signal source renderingsaid electronic switch effective to interconnect said supply and utilization circuits, a second electron discharge valve having a control electrode, means for connecting the plate of said second valve to the cathode of said first valve, means for connecting the control electrode of said second valve to said signal source thereby to render said second valve conductive substantially simultaneously with said first valve, means comprising a capacitor connected to the plate of said second valve and adapted to be charged in a predetermined manner in response to current flow through said second valve to render said second valve nonconductive, and means for charging said capacitor in a diiierent predetermined manner while said second valve is nonconductive to permit said second valve to be rendered conductive in response to the receipt ofav signal from said signal source.

15. In combination, a source of potential, utilization means, a normally non-conductive gaseous discharge device for connecting said source to said utilization means, a source of pulses, means responsive to the receipt of pulses from said source of pulses for producing an oscillatory transient corresponding to. each pulse and of substantially greater duration than said pulse, and means responsive to the production of said oscillatory transients for rendering conductive said gaseous discharge device to connect said source of potential to said utilization circuit.

16. In combination, a source of potential, uti lization means, a normally non-conductive gaseous discharge device for connecting said source to said utilization means, a source of pulses, means responsive to the receipt of pulses from said source of pulses for producing transient waves, means responsive to the occurrence of said transient waves for rendering conductive said gaseous discharge device to connect said source of potential to said utilization circuit, means responsive to. the cessation of the production of said transient waves for a predetermined time for again rendering non-conductive said gaseous discharge device, said last-mentioned means cornprisin a capacitor, means responsive to the potential supplied to said utilization means for charging said capacitor, an electron discharge valve connected in shunt with said capacitor, additional means responsive to the occurrence of saidtransient. waves for causing firing of said electron discharge valve to prevent the accumulation of a charge on said capacitor, said capacitor being permitted to charge following the cessation of the production of transient waves, and means responsive to a predetermined charge, on said capacitor for rendering non-conductive said gaseous discharge device.

17. In combination, a source of potential, utilization means, a normally non-conductive gaseous discharge device for connecting said source to said utilization means, a source of pulses, meansresponsive to the receipt of pulses from said source of pulses. for rendering conductive said gaseous discharge device to connect said source of potential to said utilization circuit, means responsive to the cessation of the production of said pulses for a predetermined time for again rendering non-conductive said gaseous discharge device, said last-mentioned means comprising a capacitor, means responsive to the potential supplied to said utilization means for charging said capacitor, an electron discharge valve connected in shunt with said capacitor, ad-

l7 ditional means responsive to the occurrence of said pulses for causing firing of said electron discharge valve to prevent the accumulation of a charge on said capacitor, said capacitor being permitted to charge following the cessation of the production of said pulses, and means responsive to a predetermined charge on said capacitor for rendering non-conductive said gaseous discharge device.

18. In combination, a potential supply circuit, a utilization circuit, an electron discharge device, means connecting said potential supply circuit, the anode-cathode space path of said device and said utilization circuit in series circuit relation, a signal source, means responsive to signals developed by said signal source for rendering said device conductive, thereby to connect said potential supply circuit to said utilization circuit through said conducting device, means responsive to the flow of current through said device for establishing an electrical quantity a predetermined interval after said device is rendered conductive, means responsive to the continued flow of signals from said signal source for preventing said electrical quantity from being established, and means responsive to the establishment of said electrical quantity in the absence of signals from said signal source for rendering said device non-conductive, thereby to disconnect said utilization circuit from said potential supply circuit. 19. In combination, a potential supply circuit, a utilization circuit, an electron discharge device, means connecting said potential supply circuit, the anode-cathode space path of said device and said utilization circuit in series circuit relation, a

signal source, means responsive to signals developed by said signal source for rendering said device conductive, thereby to connect said potential supply circuit to said utilization circuit through said conducting device, means responsive to the flow of current through said device and operative in the absence of signals from said source for a predetermined time interval for establishing an electrical quantity, said last-named means including means responsive to the continued flow of signals from said signal source for preventing said electrical quantity from being established, .and means responsive to the establishment of said electrical quantity in the absence of signals from said signal source for rendering said device non-conductive, thereby to disconnect said utilization circuit from said potential supply circuit.

20. In combination, a potential supply circuit, a utilization circuit, an electron discharge device, means connecting said potential supply circuit, the anode-cathode space path of said device and said utilization circuit in series circuit relation, a signal source, means responsive to signals developed by said signal source for rendering said device conductive, thereby to connect said potential supply circuit to said utilization circuit through said conducting device, a capacitor, means responsive to the flow of current through said devic for charging said capacitor, means for preventing said last-named means from charging said capacitor to a predetermined voltage level during the continued flow of signals from said signal source while permitting said capacitor to be charged to said voltage level in the absence of signals from said signal source, and means responsive to charging of said capacitor to said voltage level for rendering said device non-conductive, thereby to disconnect said utilization circuit from said potential supply circuit.

teat- '66 21. In combination, a potential supply circuit, a utilization circuit, an electron discharge device, having an anode, a cathode and a control grid, means connecting the anode-cathode path of said device, said potential supply circuit and said utilization circuit in series circuit relation, a signal source, means for rendering said device conductive in response to signals developed by said signal source, thereby to connect said supply circuit to said utilization circuit through said conducting discharge device, and means jointly responsive to the conduction of said discharge device and the continued absence of a signal at said signal source for a predetermined time interval for increasing the cathode potential of said discharge device by an amount sufficient to render said device nonconductive, thereby to disconnect said supply circuit from said utilization circuit.

22. In combination, a potential supply circuit, a utilization circuit, an electron discharge device having an anode, a cathode and a control grid, means connecting th anode-cathode path of said device, said potential supply circuit and said utilization circuit in series circuit relation, a signal source, means for rendering said device conductive in response to signals developed by said signal source, thereby to connect said supply circuit to said utilization circuit through said conducting ischarge device, a capacitor, means responsive to the now of current through said discharge device for charging said capacitor in a given direction and at a predetermined rate, means responsive to signals developed by said signal source for preventing said capacitor from being charged to a predetermined level by said capacitor charging means, said capacitor charging means being capable of charging said capacitor to said predetermined level in the absence of signals from said signal source, and means responsive to charging of said capacitor to said predetermined level for increasing the cathode potential of said discharge device by an amount sufficient to render said device non-conductive, thereby to disconnect said supply circuit from said utilization circuit.

23. In combination, a potential supply circuit, a utilization circuit, an electron discharge device having an anode, a cathode and a control grid, means connecting the anode-cathode path of said device, said potential supply circuit and said utilization circuit in series circuit relation, a source of pulses, mean normally biasing said device against conduction, means responsive to pulses developed by said pulse source for rendering said device conductive, thereby to connect said supply circuit to said utilization circuit, a capacitor, means responsive to the flow of current through said device for charging said capacitor in a given direction, means for discharging said capacitor to a predetermined lower level in response to pulses developed by said pulse source, and means responsive to charging of said capacitor to a predetermined upper level for increasing the cathode potential of said device by an amount sufficient to render said device non-conductive, thereby to disconnect said supply circuit from said utilization circuit.

24. In combination, a potential supply circuit, a utilization circuit, a first electron discharge device having an anode, a cathode and a control grid, means connecting the anode-cathode path of said first device, said potential supply circuit and said utilization circuit in series circuit relation, a signal source, means for rendering said first device conductive in response to signals developed by said signal source, thereby to conaerator iie'ct said supply circuit to said utilization circuit through said conducting first discharge device, a second discharge device, means for supplying anode potential to said second device concurrently with energization of said utilization circuit, means for preventing said second device from conducting upon application of anode potential thereto, a capacitor, means for charging said capacitor in a given direction in response to current flow through said first device, means responsive to signals developed by said signal source for charging said capacitor in the opposite direction, means responsive to charging of said capacitor to a predetermined level in said given direction for rendering said second device conductive, and means responsive to current flow through said second device for increasing the cathode potential of said first device by an amount suificient to render said first device non-conductive, thereby to disconnect said supply circuit from said utilization circuit.

25. In combination, a potential supply circuit, a utilization circuit, first second and third gas tubes each having an anode a cathode and a control grid, means connecting said potential supply circuit, the anode-cathode path of said first tube and said utilization circuit in series circuit relation, a signal source, means normally biasing said first tube against conduction, means responsive to signals developed by said signal source for firing said first tube, thereby connecting said potential supply circuit to said utilization circuit, means responsive to the application of potential to said utilization circuit for supplying anode potential to said second gas tube, means for preventin said second tube from firing upon the application of anode potential thereto, a capacitor connected to the anode of said third tube, means connecting the cathode of said third tube to a negative bias potential, means including a timing resistor for charging said capacitor in a given direction upon application of potential to said utilization circuit, means responsive to signals developed by said signal source for firing said third tube and charging said capacitor in the opposite direction through said third tube, said third tube being extinguished when the potential across said capacitor approaches said negative bias potential, means responsive to charging of said capacitor in said given direction to a predetermined positive level in the absence of signals from said signal source for firing said second tube, and means responsive to current fiow through said second tube for increasing the cathode potential of said first tube by an amount suificient to extinguish said first tube, thereby to disconnect said utilization circuit from said potential supply circuit.

26. In combination, a potential supply circuit, a utilization circuit, a first electron discharge device, means connecting said first device, said potential supply circuit and said utilization circuit in series circuit relation, a signal source, means for rendering said first device conductive in response to signals developed by said signal source, thereby to connect said supply circuit to said utilization circuit through said conducting first discharge device, a capacitor and resistor connected in series across said utilization circuit, said capacitor being charged to the potential applied to said utilization circuit when said first device is rendered conductive, a second electron discharge device having at least an anode and a cathode, the cathode of said second device being connected to said resistor, means jointly responsive to the conduction of said first device and the absence of signals from said signal source for rendering said second device conductive to produce a potential across said resistor, and means for applying the sum of the potentials across said capacitor and resistor to the cathode of said first device thereby to render said first device nonconductive and disconnect said utilization circuit from said potential supply circuit.

27. In combination, a source of potential, utilization means, a normally non-conductive gaseous discharge device for connecting said source to said utilization means, a source of pulses of given polarity, an electron discharge device including an input electrode and an output electrode, a highly inductive load circuit connected to said output electrode, means for impressing pulses developed by said source upon said input electrode, means for deriving from said output electrode an oscillatory transient corresponding to each of said pulses, at least a portion of each oscillatory transient being of the same polarity as said pulses and of substantially greater duration than said pulses, and means responsive to said portions of said oscillatory transients for firing said gaseous discharge device to connect said source of potential to said utilization circuit.

ROBERT B. TROUSDALE.

References Cited in the file of this patent UNITED STATES PATENTS 

